ABSTRACT

The main feature of the geothermal pattern in the Western Canada Sedimentary Basin is an increase in the value of the integral geothermal gradient (the gradient over the entire sedimentary column) from the Cordillera to the Shield. Radiogenic heat production in the sediments is about one order of magnitude less than the total heat flow. Past hydrogeological studies have shown that the permeability of the rocks and the velocity of formation waters are too low to transport the terrestrial heat from recharge areas in the southwest to discharge areas in the northeast. Also, because the area is relatively undisturbed, there are no large-scale changes in thermal conductivity of the various sediments to account for the regional distribution of the integral geothermal gradient. Therefore, the geothermal field in the Western Canada Sedimentary Basin is interpreted as being controlled on a regional scale by heat flow from the crystalline basement. The increase in basement heat flow, as expressed by the distribution of the integral geothermal gradient, can be explained by a probable combination of crustal thickness and increased radiogenic heat production by crustal rocks. The analysis of core samples from the top of the basement in Alberta indeed shows a north-northeast increase in the radiogenic heat production of Precambrian rocks.

Some "geothermal anomalies" are superimposed over the regional basin-wide trend. These anomalies may be due to granitic intrusions in the basement and/or to variable heat production in the crust. Due to the relatively small and smooth variation in thermal conductivity of the sediments, the temperature distribution at the top of the Precambrian shows a regional trend of increased values as the thickness of the sedimentary cover increases. Only at an intermediate scale is the geothermal field controlled by topography and lithology.

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